How Metamorphism Works: Low, Medium, and High Pressure/Temperature Regimes

Rocks change shape when they get squeezed or heated up, just like you might squish playdough or warm up bread in the toaster.

Imagine you leave a sandwich on the counter. It stays soft and easy to chew. In the Earth, low pressure and low temperature mean rocks barely change. They are like that sandwich: not too squished, not too hot. The minerals inside stay small and loose, similar to how sugar crystals look in a bowl.

Now imagine you sit on a pillow. It gets flatter and warmer where your weight pushes down. Medium pressure and temperature act like that sitting. Rocks here start to flatten out and their tiny mineral grains begin to grow bigger, like popcorn kernels popping open. This makes the rock stronger and more layered.

Think about the bottom of a deep swimming pool. The water pushes down hard and stays cool, but deep underground it is also very hot. High pressure and temperature are like being at the very bottom of that pool, but with intense heat. The rock gets crushed tight and baked hot. The minerals rearrange themselves into strong, shiny sheets, much like how butter melts and smooths out on warm toast.